Citric acid esters



Patented Aug. 15, 1950 CITBIC ACID ESTERS Chester M. Gooding, Staten Island, N. Y., and Hans W. Vahlteich, Edgewater, and Ralph H. Neal, North Bergen, N. J., assignors to The Best Foods, Inc., New York N. Y., a corporation of New Jersey No Drawing. Application October 9, 1947,

Serial No. 778,766

8Claims.

Another object of this invention is to provide agents which effect marked moisture retention characteristics in glyceridic oil compositions such as margarine.

Another object of this invention is to provide agents by means of which other agents, which per se are relatively insoluble or immiscible in glyceridic oils, are incorporated in such oils.

In the copendi'ng applications. S. N. 608.101, now Patent No. 2,485,631, S. N. 608,102, now Patent No. 2,485,632, and S. N. 608,380, now Patent No. 2,485,633, comparative tests are described which demonstrate that certain monoesters when incorporated in glyceridic oils markedly'retard deterioration of such oils. For example, monostearyl citrate when incorporated in corn salad oil is capable of retarding materially the developmentof rancidity oi the oil as indicated by peroxide number determinations. On the other hand, certain diesters of citric acid incorporated in margarine materially improve the moisture retention characteristics as described in the copending application S. N. 747,848, now Patent No. 2,485,634,

while certain diand tri-citric acid esters facilitate the incorporation of the monoesters in glyceridic oils as described for example in the copending application S. N. 608,102.

The monoand di-esters of citric acid of this invention are new compounds and may be emloyed as ingredients in the compositions disclosed and claimed in these copending applications. The citric acid esters of this invention have the following formula: 1 Ra Ra Z-[CrHlOsl-O- 1 .321111 2 in which Z isa member of the class consisting of hydrogen and monovalent hydrocarbon radical: having the formula:

m-d-ci. if

in which, in the Formula 1 above and in the hydrocarbon radicals (2) above, R1, R2 R3 and R4 are members selected from the class consisting of hydrogen and monovalent hydrocarbon substituents, such as alkyl or alkylene substituents, at least one of the members R1, R2, R3 and R4 being a hydrocarbon substituent, and when the ester is a monoalkyl citrate and one of the members R1, R2 and R: is an isopropyl group, the number of carbon atoms in the ester is at least 12. If the ester of citric acid be a'diester, the two hydrocarbon radicals in the Formula 1 above may be the same or different. For example, one may be a palmityl and the othera stearyl radical to comstitute palmityl stearyl citrate, or again one may be a stearyl radical and the other an oleyl radical to constitute oleyl stearyl citrate. Such diesters result from the reaction of mixed alcohols, such as a mixture of stearyl alcohol and oleyl alcohol with citric acid as described in Example 5 of the copending application S. N. 747,848.

' The hydrocarbon radicals may be connected through an ester linkage to one or both terminal carbonyl groups of the citric acid nucleus in accordance with the following formula:

o no- -o-n n- -c-o-x1 in which x and X1 are members of the class consisting of hydrogen and monovalenthydrocarbon radicals having the formula:

or alkylene substituents, at least one of the members R1, R2, R3 and R4 being a hydrocarbon substituent, and when the ester is a monoalkylcitrate and one of the members R1, R2 and R3 is an isopropyl group, the number of carbon atoms in the hydrocarbon radical is at least 6. At least one of the members X and X1 is an organic radical. In the diesters, X and X1 may be the same such as in diisopropyl citrate or different such as in oleyl stearyl citrate. In addition to the esters repre-- sented by the Formula 3 above, this invention also embraces esters in which a hydrocarbon radical is connected through an ester linkage to the carbon atom of the central carbonyl group of the citric acid nucleus.

As discussed in the copending application S. N. 747,848, dialkyl or dialkylene esters of citric acid, in which the alkyl or alkylene group has at least I 8 carbon atoms and more particularly in which the I in which R1, R2, R3 and R4 have the same meaning as heretofore defined. Preferably, the citric acid and the alcohol are reacted in proportions which favor the formation of the monoor di-ester of citric acid which is desired. As described in the copending applications, it is frequently desired to utilize a mixture of the mono-, diand tri-esters rather than employ the monoester or diester alone. For that purpose, the proportion of the citric acid and alcohol may be regulated to obtain the desired ratio of mono-, diand tri-esters in the final product, and such mixtures may be utilized without separation and isolation of the monoor di-ester. If desired, the monoor di-ester may be obtained in relatively pure form by subjecting the mixture of esters after reaction to fractional crystallization or selective extraction with a suitable solvent.

The esteriflcation of the alcohol and citric acid may be conducted by any of the well known methods employed for" the production of esters. However, it has been found desirable to produce these esters by a new method. In this method, a mono-hydric primary or secondary alkyl or alkylene alcohol conforming to the above noted formula may be reacted with citric acid mono- I hydrate, by heating to an elevated temperature,

such as 150 C. under reduced pressure until the reaction is complete. The reaction product for most purposes may be employed as such without further purification, or the monoor di-ester, or both may be obtained from the reaction product by subjection to fractional 'crystallization or selective extraction with a suitable solvent. A solvent may be used, for example, which dissolves a monoester but does not dissolve any appreciable amount of the diand tri-esters, or alternately, a solvent may be employed which dissolves the diand trl-ester but does not dissolve any appreciable quantities of the monoester. By repeating the treatment with the solvents, a relatively pure monoester of citric acid may be obtained. By the same means, the diester may be separated from the triester.

If it is desired to obtain a relatively pure monoester of citric acid, a monohydric primary alkyl or alkylene alcohol conforming to the formula noted above may be reacted with anhydrous citric acid dissolved in a solvent, such as a dry pyridine containing concentrated sulfuric acid. About 0.75% of concentrated sulfuric acid based on the weight of the reaction mixture is used as the catalyst. For this purpose, the amounts of citric acid and alcohol employed are desirably those which favor the formation of the monoester. For this purpose, an amount of citric acid in excess of that required to react with the alcohol to produce the monoester is employed. The reaction mixture is heated for a period of about four to six hours at about 100 C. after which the reaction mixture is maintained for a period of from fourteen to twenty hours at about 40 to 50 C. The resulting reaction product is then poured into a water-ice mixturepontaining a sufflcient quantity of concentrated sulfuric acid to react with the pyridine in the mixture to form pyridine sulfate. A solvent such as a low boiling petroleum ether in which the d1- and triesters are relatively soluble but in which the monoester is relatively insoluble is employed to effect a separation of the monoester from the small amounts of the diand tri-esters in the reaction mixture. The aqueous mixture is extracted first with ethyl ether in which the monoester as well as the diand trl-esters is relatively soluble. To this ethyl ether extract is added a relatively large quantity of low boiling petroleum ether in which the monoester is substantially insoluble, but in which the diand tri-esters are relatively soluble. This precipitates the monoester. If further purification is desired,

this precipitate o'r oily residue is again dissolved in ethyl ether and the procedure repeated. Relatively pure dlesters of citric acid may be prepared in a similar manner by reacting citric acid and the required alcohol in amounts which favor the formation of the diester.

The diester may be separated from any monoester or triester con tained therein by fractional crystallization with a suitable solvent, such as ethanol.

Examples of monoand di-esters of this invention are the citric acid esters of the following foaming cease substantially.

alcohols: 2 ethyl hexanol, octanols, decanols, dodecanols, hexadecanols, octadecanols, cosanols, docosanols, 2-ethyl hexenols, octenols,-decenols, dodecenols, hexadecenols, octadecenols, cosenols and docosenols.

A more comprehensive understanding of this invention is obtained by reference to the following examples;

Example 1.Mi.rture of monostearyl citrate, distearul citrate and tristearul citrate A mixture of monostearyl citrate, distearyl citrate and tristearyl citrate which may be utilized for incorporating in margarine is pre- V ture is agitated. The mixture is held at C. under reduced pressure for a period. of 1% hours. At the end of this period, boilin and The resulting product which consists of a mixture of about 10 to 15% monostearyl citrate, about 50% distearyl citrate and the remainder tristearyl citrate together with a quantity of mono-, diand tripalmityl citrates has an acid value of about 83, a saponiflcation value of about'249 and a melting point of about51 to 68C. and a color on the Lovibond scale of about 35Y-5.8R.

Example 2.-Mirture of monolauryl citrate, di-

lauryl citrate and trilauryl citrate A mixture of monolauryl citrate, dilauryl cialcohol, and 120 lbs. of anhydrous citric acid is used instead of 12.1 kilos of citric acid monohydrate. The acid value of the mixture'of about to monolauryl citrate, about dilauryl citrate and the remainder trilauryl citrate is 118 and the saponification value is 314 compared respectively with theoretical values for pure dilauryl citrate of 106 and 318 respectively.

Example 3.Pure monostearyl citrate Pure monostearyl citrate is prepared as follows:

120 grams of anhydrous citric acid is dissolved in 200 grams of refined, dry pyridine containing 1.8 grams of concentrated sulfuric acid by mechanical agitation while heating on a steam plate at about 95 C. 20 grams of pure stearyl alcohol is then introduced. The stearyl alcohol is quite insoluble in the reaction mixture,a condition favoring monoester formation since a small concentration of stearyl alcohol in solution is reacted with a large excess of citric acid. The reaction 'mixture becomes homogeneous after about 4 hours, after which time the reaction mixture is maintained at 49 to 50 C. for 16 hours.

The reaction mixture is poured into iced-water containing '75 grams of concentrated sulfuric acid. The aqueous mixture is extracted with ethyl ether and the ether extract is thoroughly washed with dilute hydrochloric acid and then with water and finally dried with anhydrous sodium sulfate. The ethyl ether solution of monostearyl citrate is evaporated, and the residue is crystalized several times from a petroleumether, the boiling range of which is 89 to 112 C.

A typical melting point of the product is from 74 to 885 C., probably depending upon the proportion of symmetrical and unsymmetrical monoesters present. Other typical characteristics are:

Found Calcd.

Acid Vnlne 246 28 Baponiflcation Value- 358 370 Example 4.Mi:rture of monoisopropz l citrate and diisopropyl citrate saponiflcation value 392 (one-half esterlfled). The alcohol and most of the water of reaction are removed by low temperature evaporation in vacuo.

The residue is taken up with ethyl ether and then thrown out of the ether solution by the addition of a quantity of low-boiling petroleum ether just suflicient to form a precipitate. The precipitate or oily residue is again taken up with ethyl ether and the precipitation with low-boiling petroleum ether repeated. This procedure is repeated several times. After final removal of solvent by heating with stirring to C., a typical analysis is:

Found Calcd.

Acid Value 454 48) Saponiflcation Value- 700 72!) Example 5.Mi1:ture comprising principally dioleyl citrate, distearyl citrate and oleylstearzll citrate A mixture of dioleyl citrate, distearyl citrate and oleylstearyl citrate is prepared as follows:

A mixture of 14 kilos of commercial oleyl alcohol and 14 kilos of commercial stearyl alcohol is melted. To this mixture is added 10.2- kilos of anhydrous citric acid. During the addition, the mixture is agitated. The mixture is heated and held for a period of 1% hours at C. under reduced pressure. At the end of this period, boiling and foaming cease substantially. The mixture contains the distearyl citrate, dioleyl citrate and their corresponding monoand tri-esters together with mixed esters containing iihtsgearyl and oleyl groups such as oleylstearyl Erample 6.M'irture of mo'nooctul citrate, dioctyl citrate and trioctyl citrate A mixture of monooctyl citrate, dioctyl citrate and trioctyl citrate is prepared as follows:

150 lbs. of octyl alcohol (commercial 2-ethyl hexanol) is heated in aclosed vessel with 137 lbs.

of anhydrous citric acid for 6 hours at 150-155' C. The reaction product comprised three layers, an upner ester laver. a middle aqueous layer and an almost crystalline sludge. The upper oily layer which comprised mono-, diand tri-octyl Example 7.Pure distearyl citrate.

.' of 76.4 and a. saponification value of 240.2 (calculated acid value 80.6 and saponiflcation value 242). Distearyl citrate; upon supercooling, ex-

7 hibits a double melting point; one at 53 C. and a second melting point at 70 to 72 C,

The terms and expressions which we have employed are used as terms of description and not or limitation, and we have no intention, in the use of such terms and expressions, of excluding any equivalents of the features described or pottions thereof, but recognize'that various modifications are possible within the scope of the invention claimed.

What is claimed is:

1. An ester of citric acid selected from the class consisting of monoisopropyl citrate and monostearyl citrate.

2. Monoisopropyl citrate.

gamma 3. Monostearyicitrate.

- CHESTER M. GOODING.

HANS W. VAHLTEICH. RALPH H. NEAL.

REFERENCES CITED The following references are or record in th; tile 01 this patent: I

UNITED STATES PATENTS 

1. AN ESTER OF CITRIC ACID SELECTED FROM THE CLASS CONSISTING OF MONOISOPROPYL CITRATE AND MONOSTEARYL CITRATE. 